1. Field of the Invention
The present invention generally relates to apparatuses for reading data recorded on a recording medium, and more particularly to an apparatus for reading data recorded on a recording medium in which data is repetitively detected to accurately read data without deteriorating effects of a data format.
2. Description of the Related Art
As a recording medium for a data recording and reading apparatus, a magnetic disk, a magnetic tape, an optical disk, a magneto-optical disk or the like has been provided. Data are recorded on any one of the recording mediums by magnetized marks and then are permanently maintained for a longer time than data recorded on a semiconductor memory. Also, in order to manage a large amount of information such as a graphic or an image, the above recoding media are essential to record information for a computer.
For example, a conventional data recording and reading apparatus records data on a recording medium in accordance with a predetermined format as shown in FIG. 1. In the conventional data recording and reading apparatus, when a sector mark (SM) of an address information (ID) part formed by pre-pits is detected, an ID read gate signal (IDRG) is turned ON and then data recorded in the ID part are detected. When data of the ID part is detected and an optical disc controller (ODC) recognizes a target sector, the ODC applies a data (MO) read gate signal (MORG) to read data recorded on a data (MO) part.
In a configuration of a conventional read channel system as shown in FIG. 2, in a case in which the ID part is formed by pre-pits on a recording medium 10, a signal is output based on a strength of a beam reflected to a detector 19. In a case of MO data recorded on the recording medium 10, a signal is output to the detector 19 based on a rotation angle of the reflected beam. Then, the ID read gate signal or the MO read gate signal is output and a multiplexer (MUX) 13 selects a read signal for the ID part or the MO part. After the multiplexer 13 selects the read signal, a waveform of the read signal is adjusted by an amplifier (Amp) 11 or 12, an AGC (Automatic Gain Control) 14, a LPF (Low Pass Filter) 15 and an equalizer (EQ) 16. Also, an ADC (A/D converter) 18 samples the read signal by a clock synchronized at a PLL (Phase-Locked Loop) 17. Then, a PRML (Partial Response Maximum Likelihood) scheme or a recursive decoding process is conducted for sample data by the detector 19 and a decoder 20. In the conventional read channel system, the clock itself synchronized at the PLL 17 is used to detect read data. In a case of the PRML scheme in which a recursive detection is not conducted, a gap (in FIG. 1) is provided between the ID part and the MO part, for a delay time from a detection of the ID part to an output of the MO read gate signal for detecting the MO part. Thus, a data process can be consecutively conducted.
However, the configuration of the conventional read channel system has the following disadvantages:
In a conventional data detection method, a read process for reading data sampled from the read signal and a data detection process for detecting the most likelihood value from a sample value read in the read process are conducted alternately and continuously. In this case, for example, if the data detection for the ID part is recursively conducted, a time from recognition of the ID part to the output of the MO read gate signal becomes longer. Thus, if a longer gap is provided to realize the above recursive process, a format effect is deteriorated. On the other hand, without providing the longer gap, when data recorded on the MO part is recursively detected, it fails to detect data of the ID part.
As described above, in the conventional data detection method in which the read process and the detection process are conducted alternately and continuously, there is a problem that the detection process can not be conducted without effect of a process time of the read process. Thus, it is difficult to apply the above recursive process that can improve a data detection performance. The detection process is limited.